The present invention relates to a method of controlling an internal combustion engine for warm-up of catalyst of an exhaust gas treatment device.
In internal combustion engines, particularly diesel engines, an excess air ratio is reduced to increase the temperature of catalyst of an exhaust gas treatment device upon and after cold start. An example of such technique is disclosed in JP P2000-18024A published Jan. 18, 2000. According to this example, an intake throttle valve and an EGR valve are adjusted to maintain an excess air ratio falling in a range from 1.5 to 1.0 to reduce intake air charge for warm-up of catalyst of an exhaust gas treatment device. The prior art technique is satisfactory, but a need remains for improving such technique by regulating an EGR rate in close cooperation with an excess air ratio for rapid warm-up of catalyst, good emission performance and stable combustion.